Power supply apparatus, and image forming apparatus having the same

ABSTRACT

A power supply apparatus with a plurality of power supply circuits each having a piezoelectric transformer and a voltage-controlled oscillator which generates a signal at an operating frequency used to drive the piezoelectric transformer in accordance with a control signal, includes a frequency-dividing circuit which divides the operating frequency generated by a voltage-controlled oscillator in at least one power supply circuit, and outputs a signal at a driving frequency to drive a piezoelectric transformer in the one power supply circuit. When at least one power supply circuit and remaining power supply circuits output voltages, the operating frequency generated by the voltage-controlled oscillator in the one power supply circuit is controlled to be higher than the operating frequency generated by the voltage-controlled oscillator in another power supply circuit.

This application is an application for reissue of U.S. Pat. No.7,557,448, issued on Jul. 7, 2009, which is hereby incorporated byreference, as if fully set forth herein. U.S. Pat. No. 7,557,488 maturedfrom U.S. application Ser. No. 11/677,397, filed Feb. 21, 2007.

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 7,557,488. The reissue applications are U.S.application Ser. No. 13/244,966, filed Sep. 26, 2011 and which is areissue continuation of the present application Ser. No. 13/175,149,filed Jul. 1, 2011, both of which may reissue from U.S. Pat. No.7,577,488.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply apparatus suitable foran image forming apparatus which forms an image by anelectrophotographic process and, more particularly, to a power supplyapparatus using a piezoelectric transformer and an image formingapparatus using the power supply apparatus.

2. Description of the Related Art

When an image forming apparatus which forms an image by anelectrophotographic process adopts a direct transfer system oftransferring an image by bringing a transfer member into contact with aphotosensitive member, the transfer member uses a conductive rubberroller having a conductive rotating shaft. In this case, driving of thetransfer member is controlled to match the process speed of thephotosensitive member.

A voltage applied to the transfer member is a DC bias voltage. At thistime, the polarity of the DC bias voltage is the same as that of atransfer voltage for general corona discharge. To achieve satisfactorytransfer using the transfer roller, a voltage of generally 3 kV or more(the required current is several μA) must be applied to the transferroller. This high voltage necessary for the above image forming processis conventionally generated using a wire-wound electromagnetictransformer. The electromagnetic transformer is made up of a copperwire, bobbin, and core. When the electromagnetic transformer is used inapplication of a voltage of 3 kV or more, the leakage current must beminimized at each portion because the output current value is as smallas several μA. For this purpose, the windings of the transformer must bemolded with an insulator, and the transformer must be made large incomparison with the magnitude of the supply power. This inhibitsdownsizing and weight reduction of a high-voltage power supplyapparatus.

In order to compensate for these drawbacks, generation of a high voltageusing a flat, light-weight, high-output piezoelectric transformer isexamined. By using a piezoelectric transformer formed from ceramic, thepiezoelectric transformer can generate a high voltage at higherefficiency than that of the electromagnetic transformer. Sinceelectrodes on the primary and secondary sides can be spaced apart fromeach other regardless of coupling between the primary and secondarysides, no special molding is necessary for insulation. The piezoelectrictransformer brings an advantage of making a high-voltage generationapparatus compact and lightweight.

For example, Japanese Patent Laid-Open No. 11-206113 discloses ahigh-voltage generation apparatus using a piezoelectric transformer.

A high-voltage power supply circuit using a piezoelectric transformerwill be explained with reference to FIG. 13. In FIG. 13, referencenumeral 101Y denotes a piezoelectric transformer (piezoelectric ceramictransformer) for a high-voltage power supply. Diodes 102Y and 103Y and ahigh-voltage capacitor 104Y rectify and smooth an output from thepiezoelectric transformer 101Y to a positive voltage, and a transferroller (not shown) serving as a load receives it. Resistors 105Y, 106Y,and 107Y divide the output voltage, and the inverting input terminal(negative terminal) of an operational amplifier 109Y receives it via aprotection resistor 10Y. The non-inverting input terminal (positiveterminal) of the operational amplifier receives, via a resistor 114Y, ahigh-voltage power supply control signal Vcont which serves as an analogsignal and is input to a connection terminal 118Y from a DC controller201. The operational amplifier 109Y, the resistor 114Y, and a capacitor113Y construct an integrating circuit. The operational amplifier 109Yreceives control signal Vcont smoothed by an integral time constantdetermined by the component constants of the resistor and capacitor. Theoutput terminal of the operational amplifier 109Y is connected to avoltage-controlled oscillator (VCO) 110Y. A transistor 111Y whose outputterminal is connected to an inductor 112Y is driven to supply power tothe primary side of the piezoelectric transformer.

The high-voltage power supply unit of an electrophotographic imageforming apparatus comprises a plurality of high-voltage power supplycircuits using the piezoelectric transformer shown in FIG. 13. Thehigh-voltage power supply unit corresponding to image forming units for,e.g., yellow (Y), magenta (M), cyan (C), and black (BK) outputs biasesfor charging, development, transfer, and the like to form images.

In the above example, pluralities of piezoelectric transformers andcontrol circuits are arranged in the high-voltage power supply unit, anda plurality of bias voltages are output to form images. Especially, ahigh-voltage power supply unit mounted in a color image formingapparatus of a tandem system requires four bias output circuits forcharging, development, transfer, and the like in correspondence withformation of cyan, magenta, yellow, and black images. The circuitscorresponding to cyan (C), magenta (M), yellow (Y), and black (BK)colors are controlled at almost the same bias output voltage.Piezoelectric transformers mounted in the high-voltage power supply unitare driven at almost the same frequency (close frequencies) in therespective bias output circuits (C, M, Y, and BK) for charging,development, transfer, and the like.

A plurality of piezoelectric transformers are driven at closefrequencies to output the same bias voltages. In this case, adjacentpiezoelectric transformers interfere with each other via the powersupply line or depending on electrostatic capacitive coupling or thelike, which makes it difficult to improve the output precision of a highbias voltage. Alternatively, the image quality may degrade due to, e.g.,generation of fluctuations of a high bias voltage by the interferencefrequency.

In order to prevent an image from being influenced by the precision of ahigh bias voltage, piezoelectric transformers are arranged at largeintervals. In order to suppress interference via the power supply line,the pattern length is increased or the capacitance of a decouplingcapacitor is increased in designing the pattern of the power supplyline.

However, it is difficult to analyze these measures by theoreticalcalculation. Many experiments are required to determine whether theabove measures can solve the problem, and concrete measurements must betaken where possible. This prolongs the period of product development.Even when these measures can solve the problem, the high-voltage powersupply unit can hardly achieve downsizing and a high image quality atthe same time.

The present invention has been proposed to solve the conventionalproblems, and has as its object to provide a power supply apparatususing piezoelectric transformers which suppresses the interferencebetween the driving frequencies of the piezoelectric transformers,implements downsizing and a high image quality, and requires noexperimental measure.

It is another object of the present invention to provide an imageforming apparatus having the power supply apparatus.

SUMMARY OF THE INVENTION

According to the present invention, the foregoing object is attained byproviding a power supply apparatus with a plurality of power supplycircuits each having a piezoelectric transformer and avoltage-controlled oscillator which generates a signal at an operatingfrequency used to drive the piezoelectric transformer in accordance witha control signal, comprising:

a frequency-dividing circuit which divides the operating frequencygenerated by a voltage-controlled oscillator in at least one powersupply circuit, and outputs a signal at a driving frequency to drive apiezoelectric transformer in the one power supply circuit,

wherein when the at least one power supply circuit and remaining powersupply circuits output voltages, the operating frequency generated bythe voltage-controlled oscillator in the one power supply circuit iscontrolled to be higher than the driving frequency.

According to the present invention, the foregoing object is attained byproviding an image forming apparatus comprising:

the above mentioned power supply apparatus; and

an image forming unit adapted to form a toner image,

wherein the image forming unit uses a voltage supplied from the powersupply apparatus.

The present invention can provide a power supply apparatus usingpiezoelectric transformers, which suppresses the interference betweenthe driving frequencies of the piezoelectric transformers, implementsdownsizing and a high image quality, and requires no experimentalmeasurements.

The present invention can also provide an image forming apparatus havingthe power supply apparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the arrangement of a transferhigh-voltage power supply using a piezoelectric transformer according tothe first embodiment;

FIG. 2 is a view showing the arrangement of an image forming apparatushaving a high-voltage power supply apparatus using a piezoelectrictransformer according to the first embodiment;

FIG. 3 is a circuit diagram for explaining the schematic mechanism ofthe occurrence of interference, and showing the arrangement of thetransfer high-voltage power supply using the piezoelectric transformer;

FIG. 4 is a graph showing the relationship between the output voltage(V) and the driving frequency (Hz) as a characteristic of thepiezoelectric transformer;

FIG. 5 is a graph showing the relationship between the drivingfrequencies fx1 and fx2 (Hz) and the output voltage (V);

FIG. 6 is a graph showing effects obtained when the transferhigh-voltage power supply includes a frequency-dividing circuitaccording to the first embodiment;

FIG. 7 is a circuit diagram showing the arrangement of a transferhigh-voltage power supply using a piezoelectric transformer according tothe second embodiment;

FIG. 8 is a table for explaining the setting of a frequency divisionratio in the transfer high-voltage power supply using the piezoelectrictransformer according to the second embodiment;

FIG. 9A is a graph showing the relationship between a bias voltage(control output voltage Edc) and a driving frequency;

FIG. 9B is a partial enlarged view of an area 901 surrounded by a brokenline in FIG. 9A;

FIG. 10 is a circuit diagram showing the arrangement of a transferhigh-voltage power supply using a piezoelectric transformer according tothe third embodiment;

FIG. 11 is a block diagram showing the arrangement of a detectingcircuit arranged in a Y-station high-voltage circuit in the transferhigh-voltage power supply using the piezoelectric transformer accordingto the third embodiment;

FIG. 12A is a timing chart showing a signal input to a detectingcircuit;

FIG. 12B is a timing chart showing a low-pass filter output obtained bycutting off a high-frequency component;

FIG. 12C is a timing chart showing a signal output from the detectingcircuit; and

FIG. 13 is a circuit diagram showing a conventional high-voltage powersupply circuit using a piezoelectric transformer.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

The first embodiment of the present invention will be described belowwith reference to the accompanying drawings. FIG. 2 is a view showing animage forming apparatus (to be referred to as a “color laser printer”hereinafter) having a high-voltage power supply apparatus 202 using apiezoelectric transformer according to this embodiment.

A color laser printer 401 comprises a deck 402 which stores recordingpaper 32, and a deck paper presence/absence sensor 403 which detects thepresence/absence of the recording paper 32 in the deck 402. The colorlaser printer 401 also comprises a pickup roller 404 which picks up therecording paper 32 from the deck 402, and a deck paper feed roller 405which conveys the recording paper 32 picked up by the pickup roller 404.The color laser printer 401 further comprises a retarding roller 406which is paired with the deck paper feed roller 405 and preventsmulti-feed of the recording paper 32.

A registration roller pair 407 which synchronously conveys the recordingpaper 32, and a pre-registration sensor 408 which detects conveyance ofthe recording paper 32 to the registration roller pair 407 are arrangeddownstream of the deck paper feed roller 405. An electrostaticchuck/convey/transfer belt (to be referred to as “ETB” hereinafter) 409is arranged downstream of the registration roller pair 407. Images areformed on the ETB 409 by image forming units made up of processcartridges 410Y, 410M, 410C, and 410BK and scanner units 420Y, 420M,420C, and 420BK for four colors (Y, M, C, and BK). The formed images aresequentially superposed on each other by transfer rollers 430Y, 430M,430C, and 430BK to form a color image. The color image is transferredand conveyed on the recording paper 32.

A pair of a pressurizing roller 434 and a fixing roller 433 whichincorporates a heater 432 in order to thermally fix a toner imagetransferred on the recording paper 32 are arranged on the downstreamside. Further, a fixing/discharge roller pair 435 which conveys therecording paper 32 from the fixing roller, and a fixing/discharge sensor436 which detects conveyance from the fixing unit are arranged.

Each scanner unit 420 comprises a laser unit 421, and a polygon mirror422, scanner motor 423, and image forming lens group 424 for scanningeach photosensitive drum 305 with a laser beam from the laser unit 421.A laser beam emitted by the laser unit 421 is modulated based on animage signal sent from a video controller 440.

Each process cartridge 410 comprises the photosensitive drum 305, acharging roller 303, a developing roller 302, and a toner storage vessel411 which are necessary for a known electrophotographic process. Theprocess cartridge 410 is detachable from the color laser printer 401.

The video controller 440 receives image data sent from an externaldevice 441 such as a personal computer (host computer), and bitmaps theimage data into bitmap data to generate an image signal for forming animage.

Reference numeral 201 denotes a DC controller serving as the controlunit of the laser printer. The DC controller 201 is configured by an MPU(microcomputer) 207, various input/output control circuits (not shown),and the like. The MPU 207 has a RAM 207a, ROM 207b, timer 207c, digitalinput/output port 207d, and D/A port 207e.

The high-voltage power supply unit (high-voltage power supply apparatus)202 comprises a charging high-voltage power supply (not shown) and adevelopment high-voltage power supply (not shown) which correspond toeach process cartridge 410 (Y, M, C, or BK), and a transfer high-voltagepower supply which corresponds to each transfer roller 430 and uses apiezoelectric transformer capable of outputting a high voltage.

The arrangement of the transfer high-voltage power supply using thepiezoelectric transformer will be explained with reference to FIG. 1.The arrangement of the transfer high-voltage power supply (to be alsosimply referred to as a “transfer high-voltage power supply”hereinafter) using the piezoelectric transformer according to the firstembodiment is effective for both positive- and negative-voltage outputcircuits. A transfer high-voltage power supply which typically requiresa positive voltage will be explained.

The transfer high-voltage power supply includes four circuits incorrespondence with the transfer rollers 430Y, 430M, 430C, and 430BK foryellow (Y), magenta (M), cyan (C), and black (BK). These circuits havethe same circuit arrangement, and FIG. 1 illustrates two typicalcircuits for yellow (Y) and magenta (M) (the reference numeralrepresenting each circuit is suffixed with Y or M for discrimination).However, the essentials of the present invention are not limited tothese two circuits, and can also be applied to the arrangement of atransfer high-voltage power supply having four or more circuits.

The image forming apparatus according to this embodiment of the presentinvention includes a plurality of color stations which form images ofdifferent colors. The image forming apparatus includes a plurality ofhigh-voltage power supply circuits each having a piezoelectrictransformer to output a voltage to be used by each color station (Y, M,C, or BK). In the following description, the circuits are respectivelycalled a “Y-station high-voltage circuit”, “M-station high-voltagecircuit”, “C-station high-voltage circuit”, and “BK-station high-voltagecircuit”.

In FIG. 1, reference numeral 101M denotes a piezoelectric transformer(piezoelectric ceramic transformer) for a high-voltage power supply.Diodes 102M and 103M and a high-voltage capacitor 104M rectify andsmooth an output from the piezoelectric transformer 101N to a positivevoltage, and an output terminal 116M supplies it to a transfer roller(not shown) serving as a load. Resistors 105M, 106M, and 107M divide theoutput voltage, and the non-inverting input terminal (positive terminal)of an operational amplifier 109M receives it via a protection resistor108M. The inverting input terminal (negative terminal) of theoperational amplifier receives, via a series resistor 114M, ahigh-voltage power supply control signal Vcont which serves as an analogsignal from the DC controller 201 and is input from a connectionterminal 1 18M. The operational amplifier 109M, the resistor 114M, and acapacitor 113M constitute an integrating circuit.

The output terminal of the operational amplifier 109M is connected to avoltage-controlled oscillator (VCO) 11CM. The output terminal of thevoltage-controlled oscillator 110M is connected to the gate of a fieldeffect transistor 111M. The drain of the field effect transistor 111M isconnected to a power supply (+24 V: Vcc) via an inductor 112M, groundedvia a capacitor 115M, and connected to one electrode of thepiezoelectric transformer 101M on the primary side. The other electrodeon the primary side is grounded. The source of the field effecttransistor 111M is also grounded.

FIG. 4 is a graph showing the relationship between the output voltage(V) and the driving frequency (Hz) as a characteristic of thepiezoelectric transformer. As the characteristic of the piezoelectrictransformer, the output voltage generally reaches a maximum voltage Emaxat a resonance frequency f₀ as shown in FIG. 4. At a driving frequencyfx, the piezoelectric transformer outputs a specified output voltage (tobe also referred to as a “control output voltage” hereinafter) Edc. Thedistribution of the output voltage (V) forms a bell shape using, as thecenter, the resonance frequency (to be also referred to as a “maximumfrequency” hereinafter) f₀. Changing the driving frequency can controlthe output voltage. For example, to increase the output voltage of thepiezoelectric transformer, the driving frequency changes from a higherdriving frequency to a lower one toward the resonance frequency f₀. Inthe following description, control is done at a frequency higher thanthe resonance frequency f₀. The same also applies to control at a lowerfrequency.

The voltage-controlled oscillator (VCO) 110M operates to increase theoutput frequency when the input voltage rises, and decrease it when theinput voltage drops. When the control output voltage Edc of thepiezoelectric transformer 101M rises, an input voltage Vsns at thenon-inverting input terminal (positive terminal) of the operationalamplifier 109M rises due to the resistor 105M, and the voltage at theoutput terminal of the operational amplifier 109M also rises. Since theinput voltage of the voltage-controlled oscillator 110M rises, itsoutput frequency increases, and the driving frequency of thepiezoelectric transformer 100M also increases. Hence, the piezoelectrictransformer 101M is driven at a frequency higher than the drivingfrequency fx. Since the output voltage of the piezoelectric transformer101M drops as the driving frequency fx increases, the output voltage iscontrolled to a lower one. That is, the arrangement in FIG. 1 forms anegative feedback control circuit.

When the control output voltage Edc of the piezoelectric transformer101M drops, the input voltage Vsns of the operational amplifier 109Malso drops, as does the voltage at the output terminal of theoperational amplifier 109M. Since the input voltage of thevoltage-controlled oscillator (VCO) 110M drops, its output frequencydecreases, and the driving frequency of the piezoelectric transformer101M also decreases. Since the output voltage of the piezoelectrictransformer 101M rises as the driving frequency fx decreases, the outputvoltage is controlled to a higher one.

In this fashion, the output voltage is controlled to a constant voltageso as to be equal to a voltage determined by the voltage of the controlsignal Vcont which is input from the DC controller 201 to the invertinginput terminal (negative terminal) of the operational amplifier 109M.

In normal printing operation corresponding to the four, yellow (Y),magenta (M), cyan (C), and black (BK) colors, high-voltage circuits,i.e., piezoelectric transformers operate at almost the same timing sincorrespondence with the four, Y, M, C, and BK colors. In order toexplain a feature of the first embodiment, the operation of two circuitsfor yellow (Y) and magenta (M) will be explained.

As preparation for explanation, the schematic mechanism of theoccurrence of interference between two high-voltage circuits for yellow(Y) and magenta (M) will be described below with reference to FIG. 3.

The piezoelectric transformer 101Y in the Y-station high-voltage circuitin FIG. 3 is driven at a driving frequency fx1 as shown in FIG. 5, andthe piezoelectric transformer 101M in the M-station high-voltage circuitis driven at a driving frequency fx2 as shown in FIG. 5.

A line to which resistors 105Y, 106Y, 107Y, and 108Y are connectedcomprises an output voltage detection line for detecting the outputvoltage of an operational amplifier 109Y which controls the voltage of apiezoelectric transformer 101Y in the Y-station high-voltage circuit.

The output voltage detection line of the operational amplifier 109Y isarranged close to the driving signal line including 112M, 111M, and 115Mand the rectifier circuit connection line including 102M, 103M, 104M,and the like of the piezoelectric transformer 101M in the M-stationhigh-voltage circuit. In this case, capacitors 151 and 152 representedby broken lines are connected between the Y- and M-station high-voltagecircuits to form a circuit model.

The output voltage detection line of the operational amplifier 109Ywhich controls the voltage of the piezoelectric transformer 101Y in theY-station high-voltage circuit generally drops a high-voltage output(about 1 KV) to a circuit voltage (about 5 V). Hence, the impedance ofthis connection line becomes higher than that of the other circuit,thereby increasing the influence of interference.

A voltage-controlled oscillator 110Y in the Y-station high-voltagecircuit receives, via the operational amplifier 109Y, the controlfrequency component fx2 of the piezoelectric transformer 101M in theM-station high-voltage circuit, in addition to the control frequency fx1of the piezoelectric transformer 101Y.

The frequency fx1 input to the VCO circuit 110Y in the Y-stationhigh-voltage circuit is influenced by the frequency fx2 for controllingthe piezoelectric transformer 101M in the M-station high-voltagecircuit, and a ripple voltage at the interference frequency appears inthe output voltage. The interference frequency represents the differencebetween the driving frequencies of the piezoelectric transformers.Referring to FIGS. 3 and 5, the interference frequency is given as theabsolute value of the driving frequency difference corresponding to thecontrol output voltage Edc:interference frequency Fb=|fx1−fx2|  (1)

This interference causes a change in the transfer efficiency betweenyellow (Y) and magenta (M). This influence may appear as a visuallyrecognized cycle in an image in accordance with the relationship withthe process speed PS (mm/S) of the image forming apparatus, and degradethe image quality.

An interference image cycle Tb (mm) which may appear in an image inaccordance with the process speed PS (mm/S) and the interferencefrequency Fb is given byTb=process speed PS/interference frequency Fb   (2)

It is generally said that the interference image cycle Tb (mm) can bevisually recognized when it becomes 0.3 mm or more. The interferenceimage cycle causes a decrease in the quality of a printed image. For theprocess speed PS=100 mm/S and the interference frequency Fb≦300 Hz, thepitch which can be visually recognized as density unevenness in theprinted image becomes 0.3 mm or more.

For the frequency fx1=163 kHz and the frequency fx2=163.2 kHz, theinterference frequency is given from the relationship of equation (1):

$\begin{matrix}\begin{matrix}{{{interference}\mspace{14mu}{frequency}\mspace{14mu}{Fb}} = {{163 - 163.2}}} \\{= {200\mspace{14mu}{Hz}}}\end{matrix} & (3)\end{matrix}$

For the interference frequency Fb=200 Hz and the process speed PS=100mm/S, the pitch of density unevenness in the printed image is given by:Tb=100/200=0.5 mm   (4)

The circuit arrangement of the power supply apparatus according to thisembodiment of the present invention will be described below withreference to FIG. 1. The power supply apparatus according to thisembodiment includes a plurality of power supply circuits each having apiezoelectric transformer and a voltage-controlled oscillator (VCO)which generates a signal at an operating frequency used to drive thepiezoelectric transformer in accordance with a control signal. The powersupply apparatus includes a frequency-dividing circuit which divides theoperating frequency generated by the voltage-controlled oscillator (VCO)in at least one power supply circuit, and outputs a signal at a drivingfrequency used to drive the piezoelectric transformer in one powersupply circuit. When at least one power supply circuit and remainingpower supply circuits output voltages, the operating frequency generatedby the voltage-controlled oscillator in one power supply circuit iscontrolled to be higher than the driving frequency.

The circuit shown in FIG. 1 is different from the circuit used toexplain an interference model in FIG. 3 in that a frequency-dividingcircuit 141Y is arranged between the voltage-controlled oscillator (VCO)110Y and a piezoelectric transformer driving FET 111Y in the Y-stationhigh-voltage circuit. For example, the frequency division ratio of thefrequency-dividing circuit 141Y is set to 2. Accordingly, thevoltage-controlled oscillator (VCO) circuit 110Y operates at anoperating frequency twice the driving frequency of the piezoelectrictransformer 101Y. When the frequency division ratio of thefrequency-dividing circuit 141Y is K (=1, 2, 4, 8, . . . ), thevoltage-controlled oscillator (VCO) circuit 110Y operates at anoperating frequency K times the driving frequency of the piezoelectrictransformer 101Y.

In accordance with the relationship between the operating frequency ofthe voltage-controlled oscillator (VCO) and the driving frequency of thepiezoelectric transformer 101Y, the frequency division ratio can begiven byfrequency division ratio K=operating frequency of voltage-controlledoscillator/driving frequency of piezoelectric transformer   (5)

Of course, the frequency division ratio shown in FIG. 1 is not limitedto “2”, but can be set in accordance with the circuit arrangement, theoperating frequency of the voltage-controlled oscillator, and thedriving frequency of the piezoelectric transformer.

In the circuit arrangement shown in FIG. 1, similar to FIG. 3, the lineto which the resistors 105Y, 106Y, 107Y, and 108Y are connectedcomprises the output voltage detection line for detecting the outputvoltage of the operational amplifier 109Y which controls the voltage ofthe piezoelectric transformer 101Y in the Y-station high-voltagecircuit. The output voltage detection line of the operational amplifier109Y is arranged close to the driving signal line including 112M, 111M,and 115M and rectifier circuit connection line including 102M, 103M,104M, and the like of the piezoelectric transformer 101M in theM-station high-voltage circuit. The capacitors 151 and 152 are connectedbetween the Y- and M-station high-voltage circuits to form the circuitmodel.

The voltage-controlled oscillator 110Y in the Y-station high-voltagecircuit operates at a frequency (operating frequency) twice the drivingfrequency of the piezoelectric transformer 101Y. The frequency-dividingcircuit 141Y divides the operating frequency by 2 (½ times), and outputsit to the piezoelectric transformer 101Y via the FET 111Y. Thepiezoelectric transformer 101Y is driven based on the input frequency.Diodes 102Y and 103Y and a high-voltage capacitor 104Y rectify andsmoothen the output from the piezoelectric transformer 101Y, and ahigh-voltage circuit 181Y outputs a high-voltage output bias via anoutput terminal 116Y.

The resistors 105Y, 106Y, and 107Y divide the output voltage, and outputit to the non-inverting input terminal (positive terminal) of theoperational amplifier 109Y via the protection resistor 108Y.Additionally, the capacitors 151 and 152 represented by broken linessuperimpose and input a voltage component based on the driving frequencyfx2 of the piezoelectric transformer 101M in the M-station high-voltagecircuit.

The inverting input terminal (negative terminal) of the operationalamplifier receives a high-voltage power supply control signal Vcontserving as an analog signal, from the DC controller 201 via a connectionterminal 118Y and series resistor 114Y. When dividing the frequency by K(frequency division ratio K (=1, 2, 4, 8, . . . )), the DC controller201 can output the high-voltage power supply control signalcorresponding to the frequency division ratio K to the inverting inputterminal (negative terminal).

It is well known that when a spurious component (a component generatedby interference between circuits) of the signal whose frequency has notbeen divided is −A (dB), the spurious component becomes −A−20·log K (dB)after dividing the frequency of the signal by K, thereby reducing theinfluence of the spurious component by K.

FIG. 6 is a graph showing the effects obtained when the transferhigh-voltage power supply includes the frequency-dividing circuit 141Yaccording to the first embodiment. Reference numeral 601 in FIG. 24denotes a ripple voltage Vrp1 in the output voltage as a function of theinterference frequency Fb (Hz) between the frequencies fx1 and fx2without performing frequency division. The ripple voltage 602 isobtained by dividing the frequency by 2, a ripple voltage 603 isobtained by dividing the frequency by 4, and a ripple voltage 604 isobtained by dividing the frequency by 8. Referring to FIG. 6, thefrequency-dividing circuit 141Y is arranged to drop the ripple voltageVrp1. The higher the frequency division ratio, the flatter the peak ofthe ripple voltage. That is, the frequency-dividing circuit 141 Y isarranged to reduce the influence of the spurious component. Thefrequency-dividing circuit 141 Y whose frequency division ratio is 2 isarranged to decrease the spurious component of the output voltage of thevoltage-controlled oscillator (VCO circuit) 110Y to about ½, and halvethe ripple voltage value output from the output terminal 116Y.

Although the frequency division ratio of a frequency-dividing circuit141 is set to “2” in the circuit arrangement of the power supplyapparatus according to this embodiment, the frequency division ratio canbe set to 1, 2, 4, 8, . . . as described above with reference to FIG. 6.Although the Y-station high-voltage circuit includes thefrequency-dividing circuit 141Y in this embodiment, the M-, C-, andBK-station high-voltage circuits may include respectivefrequency-dividing circuits. In this case, the frequency division ratiosof the frequency-dividing circuits can be different from each other.

In the power supply apparatus according to this embodiment, even whendriving the piezoelectric transformers 101Y and 101M in the high-voltagecircuits at close frequencies, the output ripple voltage value candecrease so as to form a preferable image with a small influence frominterference.

Additionally, this embodiment can provide a power supply apparatus usingthe piezoelectric transformers which suppress the influence ofinterference between the driving frequencies of the piezoelectrictransformers, implement down-sizing and a high image quality, andrequire no experimental measure.

Second Embodiment

In the first embodiment, the high-voltage circuit with thefrequency-dividing circuit, e.g., 141Y can effectively decrease theoutput ripple voltage value. In the second embodiment, an enginecontroller (DC controller) 201 can set the frequency division ratio of afrequency-dividing circuit.

FIG. 7 is a circuit diagram showing the arrangement of a transferhigh-voltage power supply using a piezoelectric transformer according tothe second embodiment. The same reference numerals as in FIG. 1according to the first embodiment denote the same parts in FIG. 7. Inaddition, a high-voltage circuit 181M outputs a high-voltage output biasvia an output terminal 116M.

The output voltage detection line of an operational amplifier 109Y isarranged close to the driving signal line including 112M, 111M, and 115Mand a rectifier circuit connection line including 102M, 103M, 104M, andthe like of a piezoelectric transformer 101M in an M-stationhigh-voltage circuit. In this case, capacitors 151 and 152 representedby broken lines are connected between the Y- and M-station high-voltagecircuits to form a circuit model. Similarly, the output voltagedetection line of the operational amplifier 109M is arranged close tothe driving signal line including 112Y, 111Y, and 115Y and a rectifiercircuit connection line including 102Y, 103Y, 104Y, and the like of apiezoelectric transformer 101Y in the Y-station high-voltage circuit.Capacitors 153 and 154 represented by broken lines are connected betweenthe M- and Y-station high-voltage circuits to form a circuit model.

A frequency-dividing circuit 141Y connected to a voltage-controlledoscillator (VCO circuit) 110Y in the Y-station high-voltage circuitcomprises a circuit capable of setting the frequency division ratio byusing an external device, such as a programmable counter. Afrequency-dividing circuit 141M connected to a voltage-controlledoscillator (VCO circuit) 110M in the M-station high-voltage circuit alsocomprises a circuit capable of setting the frequency division ratio byusing the external device, such as the programmable counter. Thefrequency-dividing circuit 141Y includes connection terminals 142Ya,142Yb, and 142Yc each of which is connected to the output port of an MPU207 mounted in the DC controller 201. The frequency-dividing circuit141M also includes connection terminals 142Ma, 142Mb, and 142Mc each ofwhich is connected to the output port of a control element (e.g., theMPU 207) mounted in the DC controller 201. In this embodiment, the MPU207 is exemplified as a main controller for setting the frequencydivision ratio. However, the present invention is not limited to this.For example, the same arrangement can be implemented by using an ASIC orother semiconductor device.

FIG. 8 is a table for explaining the setting of the frequency divisionratio in the MPU 207 of the DC controller 201. For example, when thefrequency division ratios of the frequency-dividing circuits 141Y and141M are each set to 2, the terminals 142Yc and 142Mc are set ON (ON:1), and the terminals 142Ya and 142Ma and terminals 142Yb and 142Mb areset OFF (OFF: 0) under the control of the MPU 207. The MPU 207 of the DCcontroller 201 switches the ON/OFF states of each terminal, therebysetting the frequency division ratio (1, 2, 4, 8, 16, 32, . . . , or thelike) of the frequency-dividing circuits 141Y and 141M.

The frequency division ratio is not fixed but can be selected and setfrom predetermined values (e.g., 1, 2, 4, 8, 16, 32, . . . , and thelike), thus increasing the degree of freedom of the types and,especially, the layout of the electronic components to be used whendesigning the circuit board of the transfer high-voltage power supply.

For example, since the frequency division ratio of eachfrequency-dividing circuit is set to increase the interference frequencyFb, the interference image cycle Tb can be shortened (equation (2)).This makes it possible to prevent degradation of the quality of aprinted image caused by interference of the frequency.

FIG. 9A is a graph showing the relationship between a bias voltage(control output voltage Edc) and a driving frequency. FIG. 9B is apartial enlarged view of an area 901 surrounded by a broken line in FIG.9A. As shown in FIG. 9B, the control output voltage of the Y-stationhigh-voltage circuit is set to EdcY_L, and the control output voltage ofthe M-station high-voltage circuit is set to EdcM_L. The differencebetween the control output voltages Edc of two station high-voltagecircuits is ΔEdc (see FIG. 9B).

When the Y-station high-voltage circuit outputs the control outputvoltage EdcY_L, the driving frequency of the piezoelectric transformer101Y is FxY_L. When the M-station high-voltage circuit outputs thecontrol output voltage EdcM_L, the driving frequency of thepiezoelectric transformer 101M is FxM_L. At this time, the differencebetween the driving frequencies in the Y- and M-station high-voltagecircuits is ΔFL.

When the control output voltage of the Y-station high-voltage circuitrises to EdcY_H, and the control output voltage of the M-stationhigh-voltage circuit rises to EdcM_H by environmental variation or thelike, the difference between the control output voltages is ΔEdc. Atthis time, the driving frequencies of the piezoelectric transformers inthe respective station high-voltage circuits are FxY_H and FxM_H asshown in FIG. 9B. The difference between the driving frequencies is ΔFH.When comparing the differences of the driving frequencies, ΔFH<ΔFL. Thatis, when both the control output voltages rise by environmentalvariation or the like, the difference ΔFH between the drivingfrequencies decreases. For the difference ΔFH<300 Hz and the processspeed PS=100 mm/s, the pitch which can be visually recognized as densityunevenness in a printed image becomes 0.3 mm or more (see equation (2)),and density unevenness occurs in a printed image.

In order to prevent density unevenness in the printed image when thedriving frequency difference ΔFH<300 Hz, the MPU 207 can set thefrequency division ratios of the frequency-dividing circuits 141Y and141M in accordance with the setting example shown in FIG. 8. The outputripple voltage value decreases by setting the frequency division ratio(e.g., changing the frequency division ratio from 1 to 2) to form apreferable image with a small influence of interference of the drivingfrequency.

Assume that the driving frequency difference ΔFL=500 Hz while thefrequency division ratios of the frequency-dividing circuits in the Y-and M-station high-voltage circuits are set to “1” (142Ya=142Yb=142Yc=0,and 142Ma=142Mb=142Mc=0). In this case, when the driving frequencydifference ΔFH=250 Hz by environmental variation, the MPU 207 sets thefrequency division ratio of the frequency-dividing circuit 141Y in theY-station high-voltage circuit to “2” (142Ya=142Yb=0, and 142Yc=1). Theoutput ripple voltage value can be decreased by switching the setting ofthe frequency division ratio from “1” to “2” (see FIG. 6). That is, whenthe driving frequency difference decreases, the MPU 207 sets a higherfrequency division ratio to reduce the interference energy and decreasethe influence of the output ripple voltage value.

The setting of the frequency division ratio can be controlled bystoring, in a table, the frequency division ratio to be set for thedriving frequency difference ΔEdc to each frequency-dividing circuit inadvance. When changing the setting of the frequency division ratio, theoperating frequencies of the voltage-controlled oscillators (VCOcircuits) 110Y and 110M can change depending on the setting of thefrequency division ratio. In this case, the DC controller 201 can inputthe high-voltage power supply control signal corresponding to thefrequency division ratio to the inverting input terminal (negativeterminal).

In this embodiment, the frequency division ratio is not fixed but canchange, thus increasing the degrees of freedom of the types and,especially, the layout of the electronic components to be used whendesigning the circuit board of the transfer high-voltage power supply.

Alternatively, in this embodiment, since the frequency division ratio isset depending on the layout of the electronic components and theoperation state of the circuit, the output ripple voltage drops to forma preferable image with a small influence of interference.

Additionally, this embodiment can provide a power supply apparatus usingpiezoelectric transformers which suppress the influence of interferencebetween the driving frequencies of the piezoelectric transformers,implement downsizing and a high image quality, and require noexperimental measurements.

Third Embodiment

In the second embodiment, the engine controller (DC controller) 201 canset the frequency division ratio of the frequency-dividing circuit. Inthe third embodiment, detecting circuits 143Y and 143M detect themagnitudes of the interference frequency components of the drivingfrequency of a piezoelectric transformer in one power supply circuit,and the driving frequency of a piezoelectric transformer in the otherpower supply circuit. In the following description, the setting of thefrequency division ratio of the frequency-dividing circuit is controlledbased on the detection result obtained by the detecting circuit 143Y or143M.

FIG. 10 is a circuit diagram showing the arrangement of a transferhigh-voltage power supply using a piezoelectric transformer according tothe third embodiment. The same reference numerals as in FIG. 7 accordingto the second embodiment denote the same parts in FIG. 10.

A frequency-dividing circuit 141Y connected to a voltage-controlledoscillator (VCO circuit) 110Y in a Y-station high-voltage circuitcomprises a circuit capable of setting the frequency division ratio byusing an external device, such as a programmable counter. Afrequency-dividing circuit 141M connected to a voltage-controlledoscillator (VCO circuit) 110M in an M-station high-voltage circuit alsocomprises a circuit capable of setting the frequency division ratio byusing the external device, such as the programmable counter.

The frequency-dividing circuit 141Y includes connection terminals 142Ya,142Yb, and 142Yc each of which is connected to the output port of an MPU207 mounted in a DC controller 201. The frequency-dividing circuit 141Malso includes connection terminals 142Ma, 142Mb, and 142Mc each of whichis connected to the output port of a control element (e.g., the MPU 207)mounted in the DC controller 201.

Signals input to the voltage-controlled oscillators (VCO circuits) 110Yand 110M are also input to the detecting circuits 143Y and 143M. Thesignals processed by the detecting circuits 143Y and 143M are input tothe MPU 207 of the DC controller 201 via connection terminals 144Y and144M respectively.

FIG. 11 is a block diagram showing the arrangement of the detectingcircuit 143 mounted in the Y-station high-voltage circuit. Assume thatthe M-station high-voltage circuit has the same arrangement. In thearrangement shown in FIG. 11, a signal input to the voltage-controlledoscillator (VCO circuit) 110Y is input to the detecting circuit 143Y viaa terminal 143in. The detecting circuit 143Y includes a low-pass filter(to be abbreviated as an “LPF” hereinafter) 1101Y having a cutofffrequency of 350 Hz. An amplifier (amp) 1102Y is arranged on the outputside of the LPF 1101Y. The amp 1102Y amplifies a signal LPFout fromwhich a high-frequency component has been cut off by the LPF 1101Y,i.e., a signal having only an interference frequency component. Acapacitor 1103Y removes the DC component to rectify only the ACcomponent into a DC component by using the rectification circuit made upof 1104Y to 1107Y. The DC signal is output via a terminal 143out, andthen input to the MPU 207.

Assume that the frequency division ratios of the frequency-dividingcircuits 141Y and 141M are set to 1, the driving frequency fx1 of thepiezoelectric transformer 110Y in the Y-station high-voltage circuit is163 KHz, and the driving frequency fx2 of the piezoelectric transformer101M in the M-station high-voltage circuit is 163.25 KHz. In this case,a signal having a 250-Hz difference frequency (interference frequency)between the driving frequencies fx1 and fx2 is input as the input signalto the detecting circuit 143Y. The LPF 1101Y cuts off the high-frequencycomponent of 350 Hz or more from the input signal 143in (FIG. 12A) toobtain LPFout (FIG. 12B), and the DC signal 143out shown in FIG. 12C isinput to the MPU 207.

The MPU 207 compares the voltage value of the DC signal 143out with athreshold voltage Vth as a reference for changing the setting of thefrequency division ratio. If the voltage value of the DC signal 143outis larger than the threshold voltage Vth, the MPU 207 determines thatvisible density unevenness occurs in a printed image, and changes thesetting of the frequency division ratio.

For example, when both of the frequency division ratios of thefrequency-dividing circuits in the Y- and M-station high-voltagecircuits are set to 1, the MPU 207 sets the frequency division ratio ofthe frequency-dividing circuit 141Y in the Y-station high-voltagecircuit to “2” (142Ya=142Yb=0, and 142Yc=1). As described in the firstembodiment, the frequency division ratio can be set by switching theON/OFF states of the signal applied to each terminal 142Ya, 142Yb, or142Yc. The output ripple voltage value can be decreased by changing thesetting of the frequency division ratio from “1” to “2” (see FIG. 6).That is, when the voltage value obtained by the detecting circuit 143Yis larger than the threshold voltage Vth, the MPU 207 sets a higherfrequency division ratio to reduce the interference energy and decreasethe influence of the output ripple voltage value.

In the above description, the setting of the frequency division ratiochanges in the Y-station high-voltage circuit. When the DC signalvoltage value obtained by the detecting circuit 143M is larger than thethreshold voltage Vth in the M-station high-voltage circuit, the MPU 207sets a higher frequency division ratio to reduce the interference energyand decrease the influence of the output ripple voltage value.

When changing the setting of the frequency division ratio, the operatingfrequencies of the voltage-controlled oscillators (VCO circuits) 110Yand 110M can change depending on the setting of the frequency divisionratio. In this case, the DC controller 201 can input a high-voltagepower supply control signal to the inverting input terminal (negativeterminal) in correspondence with the frequency division ratio. Thecombination of the high-voltage circuit (station) which detects themagnitude of the interference frequency component by using the detectingcircuits 143Y and 143M and the high-voltage circuit (station) which setsthe frequency division ratio can be selected under the control of the DCcontroller. For example, based on the detection results of themagnitudes of the interference frequency components in both the Y- andM-station high-voltage circuits, the settings of the frequency divisionratios of one or both of the high-voltage circuits can change.

For the process speed PS=100 mm/S and the interference frequency Fb≦300Hz, the pitch which can be visually recognized as density unevenness inthe printed image becomes 0.3 mm or more. Accordingly, the cutofffrequency of the LPF 1101Y is set to 350 Hz in this embodiment. However,for example, the cutoff frequency can also change in accordance with theprocess speed PS of the image forming apparatus. The DC controller 201can also control the cutoff frequency.

In the first to third embodiments, the image forming apparatus has beendescribed by exemplifying the transfer high-voltage power supply used ina color image forming apparatus of a tandem system. However, the imageforming apparatus to be applied to the present invention is not limitedto the color image forming apparatus, but may be a mono-chrome imageforming apparatus which forms a mono-chrome image. Any circuitarrangement shown in FIG. 1, 7, or 10 may be applied to the high-voltagepower supply apparatus 202 included in the image forming apparatus toreduce the output ripple voltage value and form a preferable image witha small influence of interference.

Note that the circuit arrangement of the transfer high-voltage powersupply described in the first to third embodiments may include discretecomponents or a semiconductor IC. For example, in the circuitarrangement of the transfer high-voltage power supply described in thefirst to third embodiments, the voltage-controlled oscillator (VCO) andfrequency-dividing circuit can include discrete components. In the powersupply apparatus in these embodiments, the voltage-controlled oscillator(VCO) and frequency-dividing circuit can also include integratedsemiconductor IC devices.

In these embodiments, the setting of the frequency division ratio is notfixed but can change, thus increasing the degree of freedom of the typesand, especially, the layout of electronic components to be used whendesigning the circuit board of the transfer high-voltage power supply.

In these embodiments, since the frequency division ratio is setdepending on the layout of the electronic components and the operationstate of the circuit, the output ripple voltage drops to form apreferable image with a small influence of interference.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-048978, filed Feb. 24, 2006, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A power supply apparatus with a plurality ofvoltage output circuits each having a piezoelectric transformer and anoscillator which generates a signal for driving the piezoelectrictransformer and for controlling an output voltage of the piezoelectrictransformer, comprising: a frequency-dividing circuit which divides afrequency of the signal generated by the oscillator in at least one ofthe plurality of voltage output circuits, and outputs a drivingfrequency signal for driving the piezoelectric transformer in said atleast one voltage output circuit, wherein the frequency of the signalgenerated by the oscillator in said at least one voltage output circuitis larger than a frequency of the signal generated by the oscillator inanother of the plurality of voltage output circuits.
 2. The apparatusaccording to claim 1, wherein the frequency-dividing circuit divides thefrequency of the signal in accordance with a frequency division ratiowhich can be arbitrarily set in accordance with a signal from anexternal device.
 3. The apparatus according to claim 1, furthercomprising a detecting circuit which detects a magnitude of aninterference frequency, wherein the frequency-dividing circuit dividesthe frequency of the signal in accordance with a frequency divisionratio which is controlled based on the interference frequency.
 4. Theapparatus according to claim 1, wherein the oscillator and thefrequency-dividing circuit include discrete components.
 5. The apparatusaccording to claim 1, wherein the oscillator and the frequency-dividingcircuit include integrated semiconductor IC devices.
 6. An image formingapparatus comprising: an image forming unit adapted to form a image; anda power supply unit adapted to output voltages to said image formingunit, wherein said power supply unit comprises a plurality of voltageoutput circuits each having a piezoelectric transformer and anoscillator which generates a signal for driving the piezoelectrictransformer and for controlling an output voltage of the piezoelectrictransformer, wherein at least one of the plurality of voltage outputcircuits has a frequency-dividing circuit which divides the frequency ofthe signal generated by the oscillator in said at least one voltageoutput circuit, and wherein the frequency of the signal generated by theoscillator in said at least one voltage output circuit is larger than afrequency of the signal generated by the oscillator in another of theplurality of voltage output circuits.
 7. The image forming apparatusaccording to claim 6, wherein said image forming unit includes aplurality of image forming stations, and wherein said plurality ofvoltage output circuits output voltages to each of said plurality ofimage forming stations.
 8. The image forming apparatus according toclaim 7, wherein each of said plurality of image forming stations is acircuit for forming a different color image.
 9. A power supplycomprising: a first and a second voltage output part which each includea piezoelectric transformer, a driving part adapted to drive thepiezoelectric transformer, and an oscillation part adapted to output afrequency signal for driving the driving part, wherein the first voltageoutput part outputs a voltage to a first process part which performs aprocess operation for forming an image, and the second voltage outputpart outputs a voltage to a second process part which differs from thefirst process part and performs a process operation for forming theimage, wherein the first process part is one of a first charging partadapted to execute a charging operation for charging a firstphotosensitive member, a first developing part adapted to execute adeveloping operation for developing a latent image formed on the firstphotosensitive member, and a first transferring part adapted to executea transferring operation for transferring an image formed on the firstphotosensitive member, the second process part is one of a secondcharging part adapted to execute a charging operation for charging asecond photosensitive member, a second developing part adapted toexecute a developing operation for developing a latent image formed onthe second photosensitive member, and a second transferring part adaptedto execute a transferring operation for transferring an image formed onthe second photosensitive member, each of the oscillation part of thefirst voltage output part and the oscillation part of the second voltageoutput part outputs the frequency signal having a frequency higher thaneach driving frequency of the driving part of the first voltage outputpart and the driving part of the second voltage output part, the firstvoltage output part includes a first frequency-dividing part adapted todivide the frequency signal output from the oscillation part of thefirst voltage output part, the second voltage output part includes asecond frequency-dividing part adapted to divide the frequency signaloutput from the oscillation part of the second voltage output part, thedriving part of the first voltage output part drives the piezoelectrictransformer in accordance with a driving signal output from the firstfrequency-dividing part, and the driving part of the second voltageoutput part drives the piezoelectric transformer in accordance with adriving signal output from the second frequency-dividing part.
 10. Thepower supply according to claim 9, wherein each of the first and thesecond voltage output parts includes a feedback part which detects avoltage output from the piezoelectric transformer and controls afrequency of the frequency signal output from the oscillation part inaccordance with the detected voltage.
 11. The power supply according toclaim 10, wherein the feedback part detects the voltage output from thepiezoelectric transformer as a lower detected voltage and feeds back thelower detected voltage to the oscillation part.
 12. The power supplyaccording to claim 11, wherein the feedback part feeds back, to theoscillation part, a comparison result between the lower detected voltageand a setting signal used for controlling the voltage output from thepiezoelectric transformer so as to become a constant voltage.
 13. Thepower supply according to claim 9, wherein a frequency of the frequencysignal is equal to or more than twice the driving frequency.
 14. Anintegrated circuit controls a power supply which comprises a first and asecond voltage output part each including a piezoelectric transformerand a driving part adapted to drive the piezoelectric transformer,wherein the first voltage output part outputs a voltage to a firstprocess part which performs a process operation for forming an image,and the second voltage output part outputs a voltage to a second processpart which differs from the first process part and performs a processoperation for forming the image, and wherein the first process part isone of a first charging part adapted to execute a charging operation forcharging a first photosensitive member, a first developing part adaptedto execute a developing operation for developing a latent image formedon the first photosensitive member, and a first transferring partadapted to execute a transferring operation for transferring an imageformed on the first photosensitive member, the second process part isone of a second charging part adapted to execute a charging operationfor charging a second photosensitive member, a second developing partadapted to execute a developing operation for developing a latent imageformed on the second photosensitive member, and a second transferringpart adapted to execute a transferring operation for transferring animage formed on the second photosensitive member, said integratedcircuit further comprising: a first oscillation part adapted to output afrequency signal to the driving part of the first voltage output part; asecond oscillation part adapted to output a frequency signal to thedriving part of the second voltage output part; wherein each of theoscillation part of the first voltage output part and the oscillationpart of the second voltage output part outputs the frequency signalhaving a frequency higher than each driving frequency of the drivingpart of the first voltage output part and the driving part of the secondvoltage output part, a first frequency-dividing part adapted to dividethe frequency signal output from the first oscillation part; and asecond frequency-dividing part adapted to divide the frequency signaloutput from the second oscillation part.
 15. The integrated circuitaccording to claim 14, wherein each of the first and the second voltageoutput parts includes a feedback part which detects a voltage outputfrom the piezoelectric transformer and controls a frequency of thefrequency signal output from the oscillation part in accordance with thedetected voltage.
 16. The integrated circuit according to claim 15,wherein the feedback part detects the voltage output from thepiezoelectric transformer as a lower detected voltage and feeds back thelower detected voltage to the oscillation part.
 17. The integratedcircuit according to claim 15, wherein the feedback part feeds back, tothe oscillation part, a comparison result between the lower detectedvoltage and a setting signal used for controlling the voltage outputfrom the piezoelectric transformer so as to become a constant voltage.18. The integrated circuit according to claim 14, wherein a frequency ofthe frequency signal is equal to or more than twice the drivingfrequency.
 19. An image forming apparatus comprising: a first processpart configured to perform a process operation for forming an image; asecond process part configured to perform a process operation forforming the image, the second process part being different from thefirst process part; wherein the first process part is one of a firstcharging part adapted to execute a charging operation for charging afirst photosensitive member, a first developing part adapted to executea developing operation for developing a latent image formed on the firstphotosensitive member, and a first transferring part adapted to executea transferring operation for transferring an image formed on the firstphotosensitive member, the second process part is one of a secondcharging part adapted to execute a charging operation for charging asecond photosensitive member, a second developing part adapted toexecute a developing operation for developing a latent image formed onthe second photosensitive member, and a second transferring part adaptedto execute a transferring operation for transferring an image formed onthe second photosensitive member, and a power supply configured toinclude a first voltage output part for outputting a voltage to thefirst process part, and a second voltage output part for outputting avoltage to the second process part, wherein the first and the secondvoltage output part each include a piezoelectric transformer, a drivingpart adapted to drive the piezoelectric transformer, and an oscillationpart adapted to output a frequency signal for driving the driving part,wherein each of the oscillation part of the first voltage output partand the oscillation part of the second voltage output part outputs thefrequency signal having a frequency higher than each driving frequencyof the driving part of the first voltage output part and the drivingpart of the second voltage output part, wherein the first voltage outputpart includes a first frequency-dividing part adapted to divide thefrequency signal output from the oscillation part of the first voltageoutput part, and the second voltage output part includes a secondfrequency-dividing part adapted to divide the frequency signal outputfrom the oscillation part of the second voltage output part, and whereinthe driving part of the first voltage output part drives thepiezoelectric transformer in accordance with a driving signal outputfrom the first frequency-dividing part, and the driving part of thesecond voltage output part drives the piezoelectric transformer inaccordance with a driving signal output from the secondfrequency-dividing part.
 20. The image forming apparatus according toclaim 19, wherein each of the first and the second voltage output partsincludes a feedback part which detects a voltage output from thepiezoelectric transformer and controls a frequency of the frequencysignal output from the oscillation part in accordance with the detectedvoltage.
 21. The image forming apparatus according to claim 20, whereinthe feedback part detects the voltage output from the piezoelectrictransformer as a lower detected voltage and feeds back the detectedvoltage to the oscillation part.
 22. The image forming apparatusaccording to claim 20, wherein the feedback part feeds back, to theoscillation part, a comparison result between the detected voltage and asetting signal used for controlling the voltage output from thepiezoelectric transformer so as to become a constant voltage.
 23. Theimage forming apparatus according to claim 19, wherein each of the firstprocess part and the second process part is a part adapted to form adifferent color image.
 24. The image forming apparatus according toclaim 19, wherein a frequency of the frequency signal is equal to ormore than twice the driving frequency.